Has it been done to please that Top player
Yeah we decided to risk ruining balance for hundreds of thousands of players just to please one player, and quickly came up with some stuff on the spot. Yolo
To be frank, your questions seem to come mostly from a "grass is greener for the red faction" mentality, but I'll do my best to answer them.
1- Various units see their veterancy being improved but riflemen is still stuck with vet1 Atnade and nothing else. Is the balance team ok with riflemen being left to require vet2 to get a proper improvement on their stat?
Because the scaling of Riflemen is fine as is. They are strong and versatile mainline infantry that get better veterancy and upgrades than others. No need to fix something that isn't broken.
-2 At the same time riflemen are the least used mainline infantry (you don't build more than 3) and the only one squad carrying the Atnade for USF, on the other hand Ostheer and OKW can field 4 grenadiers or volksgrenadiers, Ostruppen or Pfuss and all of them carrying pfaust or are available after a short and linear teching. So the question why USF cannot fight light vehicle the same way they do, they are already less squads on the field with the atnade, is it not enough?
Because the USF have armor piercing HMGs, cheap bazooka squads, an officer squad with a techless bazooka upgrade, the Stuart, the 37mm on the AA halftrack, and the best stock ATG of all factions to fight light vehicles with. It's asymmetric balance and we'd like to keep it where we can.
-3 Ambulance, I see the balance team is making effort into giving the 251 or Open truck healing mechanism or better one but the ambulance is still the worst vehicle in game and can be OS by anything on wheel. Why isn't possible to increase Ambulance health and give it some more acceleration? Or simply increase its health stat when deployed in base?
Giving the ambulance additional health or durability in base was looked into but didn't seem possible. Giving the ambulance increased durability itself is a hard no because a forward ambulance rush is really strong in team games and it needs to be vulnerable to balance that. It sucks that it's so easy to dive in the main base, but there doesn't seem to be a way to prevent that. At least an evacuated medics squad will now be significantly more useful, but you seem to have ignored that change.
-4 Kubel is the bane of riflemen, if it catch you out of cover you bleeding like a stuff pig and at the same time for the same reason you can't push it. The kubel is being buffed and at the same time Rear Echelon are going to be worst vs it. How USF is going to be vs a said kubel push strat where Sturm are going to repair it faster than you can damage it.
There's plenty of things that can help counter a Kubel. M2HBs, an M20, an AAHT, the Rear Echelon light mines or just get a blob going, avoid it or fight it from green cover. It's okay that certain units require a certain effort in order to go down, that's not any different for Universal Carriers or M3 Scout Cars for example. If a Kubel is giving you trouble, adjust your strategy.
-6 USF Officers used to be crutch units and disposed from that status to be today marginally out of the box better riflemen squads. Their only crutch today is that they don't need to wait for weapon unlock to get 1 BAR or 1 Zook.
Get free squads with teching and then complain they aren't good enough? Yes, the Officer squads are a double edged sword, at least the second one, but they are still better Riflemen in most aspects, because of their (essentially free) cost and they also get 1 Thompson with pretty decent DPS. The fact that they can get an upgrade without the weapon racks tech is great for bridging the gap. I know a lot of players consider double Officer strats to be borderline overpowered because of how manpower economy efficient they are.
-7 Why did it require a Top player's comment on a popular stream for the balance team to quickly patch the patch (olol) with something about riflemen. Has it been done to please that Top player or the balance team suddenly acknowledge there is something wrong with the unit and faction.
The changes for Riflemen and RET were already discussed way earlier, but we weren't entirely convinced they were needed and we initially wanted to wait until we saw the full extend of the OKW changes and the impact on USF's early game before changing USF's early game at the same time. DevM's comment was only just one needle in the haystack of initial feedback that made us just tip over in the other direction and include the changes in the follow up patch.